008---组件的 生命周期、InitializingBean, DisposableBean接口、JSR-250规范、BeanPostProcessor接口

spring中的bean生命周期：

构造 => 初始化前 => 初始化 => 初始化后 => 销毁 

方式一：普通的java类，自定义初始化方法和销毁方法 

@Bean 可以指定初始化和销毁 回调方法，如下示例

普通的java类：

package bean;

public class HelloWorld {
    String hello="Hello demo";

    public HelloWorld() {
        super();
        System.out.println("导入成功");
    }
    //初始化方法
    public void init(){
        System.out.println("初始化。。。");
    }
    //销毁方法
    public void destory(){
        System.out.println("销毁。。。");
    }

    @Override
    public String toString() {
        return "HelloWorld{" +
                "hello='" + hello + '\'' +
                '}';
    }
}

@Bean注解配置的方式：  指定初始化 和 销毁 的回调函数

package config;

import bean.HelloWorld;
import org.springframework.context.annotation.*;

@Configuration
public class Config {

    @Bean(initMethod = "init",destroyMethod = "destory")
    public HelloWorld helloWorld(){
        return new HelloWorld();
    }

}

 方式二：实现接口的方式（InitializingBean, DisposableBean）

使用spring提供的接口实现初始化和销毁

package config;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

@Component
public class DemoInit implements InitializingBean, DisposableBean {
    //销毁
    @Override
    public void destroy() throws Exception {
        System.out.println("DemoInit销毁");
    }

    //初始化
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("DemoInit初始化");
    }
}

测试：配置类用@ComponentScan扫描将组件扫描进spring IOC容器中

package config;

import org.springframework.context.annotation.*;
@ComponentScan(value = "config")
@Configuration
public class Config {


}

测试类： 

package config;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;


import static org.junit.Assert.*;

public class ConfigTest {

    @Test
    public void test1(){
        //初始化容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Config.class);

        //销毁容器
        applicationContext.close();
    }
}

方式三：使用JSR-250规范注解（@PostConstruct、@PreDestroy）

首先导入jsr-250的jar包相关依赖

<!-- https://mvnrepository.com/artifact/javax.annotation/jsr250-api -->
        <dependency>
            <groupId>javax.annotation</groupId>
            <artifactId>jsr250-api</artifactId>
            <version>1.0</version>
        </dependency>

示例代码

package config;

import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@Component
public class DemoInit2 {

    public DemoInit2() {
    }
    @PostConstruct
    public void init(){
        System.out.println("初始化bean");
    }

    @PreDestroy
    public void destory(){
        System.out.println("销毁bean");
    }
}

和方式二的结果一样 

方式四：实现BeanPostProcessor接口(初始化的前后)

package config;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class DemoInit3 implements BeanPostProcessor {
    public Object postProcessBeforeInitialization(Object o, String s) throws BeansException {
        System.out.println(o+"=>"+s);//打印bean初始化前的全类名和名称
        return o;
    }

    public Object postProcessAfterInitialization(Object o, String s) throws BeansException {
        System.out.println(o+"=>"+s);//打印bean初始化前的全类名和名称
        return o;
    }
}